The present invention relates to mechanically actuated color displays. More particularly, the present invention relates to microelectromechanical displays using rotating colored prisms as display elements.
Passive displays based on backlit liquid crystals, or active displays based on light generative light emitting diodes or thin film transistors, are widely used in conjunction with electrical devices or computing technologies requiring status displays or user monitoring capability. Such displays are inexpensive, and manufacturable in sizes generally ranging from less than 1 square centimeter to several thousand square centimeters (with hundreds to millions of pixels). Unfortunately, both active and passive displays require a continuous source of power to maintain a display image, making them unsuitable for many low power applications where only battery power (or other low power voltage source, e.g. photovoltaic) is available. Further, in many high ambient light environments, both active and passive displays can be difficult to view, since they are generally low contrast and have a limited preferred viewing angle.
Accordingly, the present invention provides a high contrast display technology that does not require power to maintain a particular image, making it particularly suitable for use in conjunction with low power electronic or computational devices. The present invention is manufacturable using conventional microelectromechanical techniques, and pixel switching is fast enough to replace conventional active or passive displays. Further, in certain embodiments, displays in accordance with the present invention can support one bit displays (black or white), gray scales, or even colored displays. In other embodiments, non-electrical power sources can even be used to enable pixel switching, further reducing reliance on batteries.
One embodiment of the present invention provides an electrostatically controlled mechanical pixel useful for visual displays. The display array is constructed so each element of the array includes a background substrate divided into a first region and a second region, with each region having distinct light reflectance characteristics. A flap is movable between a first position blocking at least a portion of the first region of the background substrate and a second position blocking at least a portion of the second region of the background substrate. The flap can be constructed of polysilicon rotatably attached with hinges to the background substrate, and manufactured using conventional semiconductor etching techniques. A flap catchment mechanism, typically electrostatic, is used for alternatively facilitating movement of the flap between the first and second position. To actually move the flap into a position allowing flap catchment, an impulse mechanism is employed to move the flap away from one of the first or second positions. The impulse mechanism can be electrostatic based, and can be separate or combined with the flap catchment mechanism.
In certain preferred embodiments, each mechanical pixel of the display array is bistable and electrostatically controlled, with the flap catchment mechanism including a first conductive plate positioned in the first region of the background substrate and a second conductive plate positioned in the second region of the background substrate. The impulse mechanism includes a transparent sheet electrostatically chargeable to attract the flap, with the transparent sheet positioned in parallel spaced apart relationship to the background substrate to define a cavity, and with the flap attached to the background substrate to movably extend into the cavity in response to electrostatic attraction by the transparent sheet.
In operation, a user perceptible display requiring little or no power for display maintenance is available since the background substrate has a first defined light reflection characteristic, while the flap has a second defined light reflection characteristic differing from the first defined light reflection characteristic. Because the flap is positioned adjacent to the background substrate and movable to a first position covering at least a portion of the background substrate, various patterns, including text, symbols, digital images can be displayed. Depending on ambient lighting, available power, size of flaps, flap reflection characteristics, flap switching speeds, display arrays rivaling conventional LCD display arrays but requiring substantially less electrical power for operation can be created in accordance with the present invention.
To even further minimize requirements for continuous electrical power, one embodiment of the present invention provides a display array based on bistable pixels with flap switching controlled at least in part by air flow provided by pressurized cylinders or other suitable pressure sources. Such a low electrical power display array element includes a background substrate, a flap attached for movement with respect to the background substrate, and a flap catchment mechanism for alternatively facilitating movement of the flap between the first and second position. A fluid conduit is defined in part by the background substrate, with the fluid conduit permitting direction of fluid against the flap to move the flap away from one of the first and second positions. The fluid conduit is connectable to a pneumatic pressure source for directing air against the flap when the flap is in one of its first and second positions.
In one embodiment, the fluid conduit is attached to a pneumatic pressure source for directing air substantially parallel to the flap when it is in one of its first and second positions. This creates low pressure conditions that lift the flap away from the background substrate, allowing air flow between the flap and the background substrate to flip the flap between positions. The flap catchment mechanism is a mechanical, electromagnetic, electrostatic, pneumatic, or other suitable mechanism that transiently holds the flap in a desired position during air flow. For example, an electrostatic catchment can include a first conductive plate positioned in a first region of the background substrate and a second conductive plate positioned in a second region of the background substrate, with either plate electrostatically attracting and holding the flap. This combination of low-power flap-catchment mechanism and non-electrical flap impulse mechanism reduces total electrical switching costs, and is especially useful for portable or battery powered displays.
Using the foregoing described bistable display elements, various combinations of background substrate/flap colors can be used to create gray scale or colored displays with desired brightness/resolution. For example, a display array can be constructed to have a background substrate divided into an array of alternating first region and second regions, each region having differing light reflectance characteristics. A plurality of flaps is attached to the background substrate, with each flap attached at a hinge positioned at a boundary between alternating first and second regions, and with each flap movable between a first position blocking at least a portion of the first region of the background substrate and a second position blocking at least a portion of the second region of the background substrate. Each flap is constructed to have a first and a second side with differing light reflectance characteristics (e.g. white/black, white/gray, gray/black).
In certain embodiments, each flap is attached to the background is substrate by a hinge positioned at a boundary between every other alternating first and second regions, while in other embodiments each flap is attached to the background substrate by a hinge positioned at a boundary between every alternating first and second regions, allowing overlap of adjacent flaps. For example, a display array can be constructed by dividing a background substrate into an array of alternating black (B) and white (W) regions. Hinges (H) are then attached to the background substrate to form a repeating pattern BHWBHW, while each hinge attached flap is movable between a first position blocking one black (B) region and a second position blocking one white (W) region. Alternatively, the hinges (H) can be attached to the background substrate to form a repeating pattern BHWHBHWH, with the flaps movable between a first position blocking one black (B) region and a second position blocking one white (W) region. In both alternatives, each flap has a first and a second sides, the respective side of each flap having differing light reflectance characteristics, ranging from an extreme of black/white, to various grayscale or color combinations.
Adjustments to resolution, gray scale range, or switching efficiency in bistable flap elements according to the present invention are possible with careful selection of flap shape geometry. For example, a suitable display array can include a background substrate divided into multiple regular tiles. The multiple regular tiles can be covered with flaps shaped and sized to match one corresponding regular tile, with each flap positionable with respect to the background substrate to be movable between a first position completely blocking viewing of one corresponding regular tile and a second position completely blocking viewing of an adjacent corresponding regular tile. The flaps are normally constructed to have first and a second sides, with the respective side of each flap having differing light reflectance characteristics.
Various patterns or layouts of multiple regular tiles can be used. In preferred embodiments, each multiple regular tile has identical shape and size. Suitable tiling patterns include square, triangular, or hexagonal tilings (or subdivisions thereof, e.g. half a hexagon, rectangular or triangular divisions of a square, or triangular divisions of a hexagon) that completely cover a plane surface. For certain embodiments, two or more distinct regular tiles having differing sizes and shapes can be used for flap patterns. Also within the scope of the present invention are non-plane covering patterns, including disjoint tilings with gaps to allow for layout of electrical contacts or fluid conduits.
In still another embodiment of the invention particularly suitable for color displays, a non-flap variant of a mechanical pixel that provides tri-color switching using rotating solid. A display array element includes a substrate and a prism rotatably attached to the substrate. The prism has at least a first viewable surface having first reflectance characteristics and a second viewable surface having second reflectance characteristics, and in a most preferred embodiment has a third viewable surface having third reflectance characteristics. A fluid conduit is defined in part by the substrate, with the fluid conduit permitting direction of fluid against the prism to rotate the prism to selectively allow viewing of one of the first and second viewable surfaces.
Typically, the fluid conduit is attached to a pneumatic pressure source for directing air substantially parallel to one of the first, second or third viewable surfaces of the prism. A rotation catchment mechanism can be attached to limit rotation of the prism. Typically each viewable surface provides a distinct gray level, which can range from white to black. Alternatively, multiple primary or secondary additive colors can be used to respectively color each viewable surface.